Paul Osborne, AAP Senior Political Writer

The opposition has claimed Labor is looking at tax rises to fill a hole in the budget and fulfil major spending promises such as the National Disability Insurance Scheme (NDIS) and extra school funding.

Shadow treasurer Joe Hockey told reporters the government was creating "uncertainty for business and consumers" by looking at changes to superannuation and personal income tax increases.

Now a spokesman for Mr Swan has told AAP: "The government rules out personal income tax rises."

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Earlier on Thursday, Mr Swan was asked four times on ABC Radio National's breakfast program whether income tax would go up in the May 14 budget.

"I'll leave the speculation for everybody else," the treasurer said.

He later issued a statement saying speculation about personal income tax rises was "ridiculous and absurd" and that the government's record on income tax "couldn't be more clear".

Mr Swan said Labor had delivered personal income cuts worth $47 billion in three consecutive budgets and highlighted its decision to triple the tax-free threshold to $18,000.

He said the coalition was proposing to scrap the threshold change, which is being funded through the carbon tax that Opposition Leader Tony Abbott wants to repeal if the coalition wins government.

"Make no mistake, the only party advocating an increase to income tax at this election is Tony Abbott's Liberals," Mr Swan said in his statement.

Mr Hockey said on Thursday the coalition was "not in the business of increasing personal income tax".

"We don't do that," Mr Hockey said.

Asked to rule out income tax rises under a coalition government, Mr Abbott said: "I absolutely guarantee to the Australian people that the tax burden will be less under a coalition government."

The coalition would fund tax cuts and benefit increases without a carbon tax.

"We are looking at sensible, intelligent expenditure reductions ... that will enable us to provide genuine tax relief to the Australian people," he told reporters in Queanbeyan.

Mr Swan concedes a forecast 2012/13 budget surplus is now unlikely on the back of revenue writedowns, including a big shortfall in Labor's mining tax.

Analysts estimate the upcoming deficit could be around $12-15 billion.

However, Mr Swan has said the initiatives such as the NDIS will be funded.